The present invention generally relates to mounting an electronic device directly on a substrate when there is a mismatch between the thermal properties of the material making up the electronic device and the thermal properties of the material making up the substrate. More particularly, the present invention relates to mounting an electronic device, such as a semiconductor chip made primarily of silicon, directly on an organic substrate, such as printed circuit board made primarily of glass cloth impregnated with epoxy resin or other such material.
It is often desired to mount an electronic device directly on a substrate as described above when there is a mismatch between the thermal properties of the material making up the electronic device and the thermal properties of the material making up the substrate. For example, an electronic circuit board may be constructed by soldering the leads (terminals) on electronic devices, such as semiconductor chips made primarily of silicon or semiconductor chip carriers (modules) made primarily of a ceramic material, to fixed conductive circuit lines on the surface of a printed circuit board made primarily of an organic material, such as glass cloth impregnated with epoxy resin or other such material, having a thermal coefficient of expansion which is significantly different from the thermal coefficient of expansion of the material(s) making up the electronic device. If excessive stress is applied to such an electronic circuit board, for example, due to thermal cycling during the manufacture or use of the circuit board, this may damage the solder joints between the electronic device and the circuit lines on the circuit board thereby possibly allowing the electronic device to break free from the circuit board or causing other such undesirable problems.
Certain stress relief techniques are known for use in mounting electronic devices on circuitized substrates as disclosed in U.S. Pat. Nos. 4,413,308, 4,048,438, and 4,026,759. Also, see the article by L. F. Miller, "Flexible Chip Joints", IBM Technical Disclosure Bulletin, Vol. 11, No. 9, p. 1173, February 1969. However, these known techniques are complex in requiring, for example, a hole in a printed circuit board wherein an electronic device is to be mounted as disclosed in U.S. Pat. No. 4,413,308. Also, these known techniques do not specifically address mounting an electronic device made primarily of a material(s), such as silicon, directly on an organic substrate, such as a glass cloth impregnated with epoxy resin or other such material, having a thermal coefficient of expansion which is significantly different from the thermal coefficient of expansion of the material(s) making up the electronic device.